Near-field spectroscopy of Dirac plasmons in Bi2Se3 ribbon arrays

Plasmons supported in the massless electron surface states of topological insulators (TIs), known as Dirac plasmons, have great potential next generation optoelectronics. However, their inherent confinement to makes investigation plasmons challenging. Near-field techniques provide ideal platform directly probe due sensitivity evanescent fields at surface. Here, we demonstrate use aperture near-field spectroscopy for localized terahertz (THz) plasmon resonances Bi2Se3 ribbon arrays with widths ranging from 10 40 µm. Unlike scattering THz techniques, method is most sensitive relevant lower-momenta corresponding wavelengths on scale ∼20 The combination time-domain and microscopy enables sampling zone 0.5–2.5 range. We map dispersion, which reveals a coupled plasmon–phonon polariton interaction. spectra show higher contrast upper branch comparison far-field observations. information revealed by could deepen our understanding behavior leading development real-world TI devices.